Using antiferromagnets as active elements in spintronics requires the ability to manipulate and read-out the Néel vector orientation. Here we demonstrate for Mn2Au, a good conductor with a high ordering temperature suitable for applications, reproducible switching using current pulse generated bulk spin-orbit torques and read-out by magnetoresistance measurements. Reversible and consistent changes of the longitudinal resistance and planar Hall voltage of star-patterned epitaxial Mn2Au(001) thin films were generated by pulse current densities of ≃107 A/cm2. The symmetry of the torques agrees with theoretical predictions and a large read-out magnetoresistance effect of more than ≃6% is reproduced by ab initio transport calculations.

In the field of antiferromagnetic (AFM) spintronics, information about the Néel vector, AFM domain sizes, and spin-flop fields is a prerequisite for device applications but is not available easily. We have investigated AFM domains and spin-flop induced changes of domain patterns in Mn 2 Au(001) epitaxial thin films by X-ray magnetic linear dichroism photoemission electron microscopy (XMLD-PEEM) using magnetic fields up to 70 T. As-prepared Mn 2 Au films exhibit AFM domains with an average size ≤1 µm. Application of a 30 T field, exceeding the spin-flop field, along a magnetocrystalline easy axis dramatically increases the AFM domain size with Néel vectors perpendicular to the applied field direction. The width of Néel type domain walls (DW) is below the spatial resolution of the PEEM and therefore can only be estimated from an analysis of the DW profile to be smaller than 80 nm. Furthermore, using the values for the DW width and the spin-flop field, we evaluate an in-plane anisotropy constant ranging between 1 and 17 µeV/f.u.. arXiv:1803.03022v1 [cond-mat.mtrl-sci]

The effects of current induced Néel spin-orbit torques on the antiferromagnetic domain structure of epitaxial Mn2Au thin films were investigated by X-ray magnetic linear dichroism -photoemission electron microscopy (XMLD-PEEM). We observed current induced switching of AFM domains essentially corresponding to morphological features of the samples. Reversible as well as irreversible Néel vector reorientation was obtained in different parts of the samples and the switching of up to 30 % of all domains in the field of view of 10 µm is demonstrated. Our direct microscopical observations are compared to and fully consistent with anisotropic magnetoresistance effects previously attributed to current induced Néel vector switching in Mn2Au. PACS numbers:In antiferromagnetic (AFM) spintronics the staggered magnetization, or more precisely the Néel vector describing the spin structure, can be used to encode information [1][2][3]. For the switching of the Néel vector and the read-out of its orientation different strategies have been pursued [4]. The Néel vector was e. g. manipulated by an exchange-spring effect with a ferromagnet (FM) and read-out via tunneling anisotropic magnetoresistance (T-AMR) measurements [5,6]. Other experiments were based on a ferromagnet to AFM phase transition [7] or on strain induced anisotropy modifications [8]. However, for antiferromagnetic spintronics Néel vector switching by current-induced spin-orbit torques (SOTs) [9], whose FM counterparts are already established for memory applications [10,11], are most promising due to superior scaling, switching speed and device compatibility.The SOTs used for FM spintronics are typically generated at interfaces with heavy metals [12,13]. However, a specific crystallographic structure with oppositely broken inversion symmetry on the each of the collinear AFM sublattices makes Mn 2 Au and CuMnAs up to now the only known antiferromagnets, for which a so called bulk Néel spin-orbit torque (NSOT) [14] can enable current induced Néel vector manipulation in a single layer system. Indeed, this was demonstrated experimentally for CuMnAs [15,16] and, more recently, for Mn 2 Au [17][18][19] as well.Whereas in the case of CuMnAs, the modification of the AFM domain structure by current pulses was observed directly by X-ray magnetic linear dichroism -photoelemission electron microscopy (XMLD-PEEM) [16,20], such microscopic insights are missing for Mn 2 Au up to now. However, direct imaging of the effect of current pulses on the Néel vector orientation is crucial for the interpretation of previously published results of resistivity changes attributed to a Néel vector reorientation in Mn 2 Au [17][18][19]. Furthermore, magnetic microscopy enables the identification of important quantities and mech-anisms of the Néel vector manipulation such as switched volume fraction, morphological influence on the domain pattern, and domain wall motion.In this paper we demonstrate the imaging of current induced modifications of the AFM domain structure of epitaxial Mn 2 Au thin film...

The coupling of real and momentum space is utilized to tailor electronic properties of the collinear metallic antiferromagnet Mn 2 Au by aligning the real space Néel vector indicating the direction of the staggered magnetization. Pulsed magnetic fields of 60 T were used to orient the sublattice magnetizations of capped epitaxial Mn 2 Au(001) thin films perpendicular to the applied field direction by a spin-flop transition. The electronic structure and its corresponding changes were investigated by angular-resolved photoemission spectroscopy with photon energies in the vacuum-ultraviolet, soft and hard X-ray range. The results reveal an energetic rearrangement of conduction electrons propagating perpendicular to the Néel vector. They confirm previous predictions on the origin of the Néel spin-orbit torque and anisotropic magnetoresistance in Mn 2 Au, and reflect the combined antiferromagnetic and spin-orbit interaction in this compound leading to inversion symmetry breaking.

Metallic antiferromagnets with broken inversion symmetry on the two sublattices, strong spin-orbit coupling, and high Néel temperatures offer alternative opportunities for applications in spintronics. Especially Mn 2 Au, with a high Néel temperature and high conductivity, is particularly interesting for real-world applications. Here, manipulation of the orientation of the staggered magnetization, (i.e., the Néel vector) by current pulses was recently demonstrated, with the readout limited to studies of anisotropic magnetoresistance or x-ray magnetic linear dichroism. Here we report on the in-plane reflectivity anisotropy of Mn 2 Au(001) films, which are Néel vector aligned in pulsed magnetic fields. In the near-infrared region, the anisotropy is approximately 0.6%, with higher reflectivity for the light polarized along the Néel vector. The observed magnetic linear dichroism is about 4 times larger than the anisotropic magnetoresistance. This suggests the dichroism in Mn 2 Au is a result of the strong spin-orbit interactions giving rise to anisotropy of interband optical transitions, which is in line with recent studies of electronic band structure. The considerable magnetic linear dichroism in the near-infrared region could be used for ultrafast optical readout of the Néel vector in Mn 2 Au.

We observe the excitation of collective modes in the terahertz (THz) range driven by the recently discovered Néel spin-orbit torques (NSOTs) in the metallic antiferromagnet Mn_{2}Au. Temperature-dependent THz spectroscopy reveals a strong absorption mode centered near 1 THz, which upon heating from 4 to 450 K softens and loses intensity. A comparison with the estimated eigenmode frequencies implies that the observed mode is an in-plane antiferromagnetic resonance (AFMR). The AFMR absorption strength exceeds those found in antiferromagnetic insulators, driven by the magnetic field of the THz radiation, by 3 orders of magnitude. Based on this and the agreement with our theory modeling, we infer that the driving mechanism for the observed mode is the current-induced NSOT. Here the electric field component of the THz pulse drives an ac current in the metal, which subsequently drives the AFMR. This electric manipulation of the Néel order parameter at high frequencies makes Mn_{2}Au a prime candidate for antiferromagnetic ultrafast memory applications.

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Hybrid organic–inorganic networks that incorporate chiral molecules have attracted great attention due to their potential in semiconductor lighting applications and optical communication. Here, we introduce a chiral organic molecule (R)/(S)-1-cyclohexylethylamine (CHEA) into bismuth-based lead-free structures with an edge-sharing octahedral motif, to synthesize chiral lead-free (R)/(S)-CHEA4Bi2Br x I10–x crystals and thin films. Using single-crystal X-ray diffraction measurements and density functional theory calculations, we identify crystal and electronic band structures. We investigate the materials’ optical properties and find circular dichroism, which we tune by the bromide–iodide ratio over a wide wavelength range, from 300 to 500 nm. We further employ transient absorption spectroscopy and time-correlated single photon counting to investigate charge carrier dynamics, which show long-lived excitations with optically induced chirality memory up to tens of nanosecond timescales. Our demonstration of chirality memory in a color-tunable chiral lead-free semiconductor opens a new avenue for the discovery of high-performance, lead-free spintronic materials with chiroptical functionalities.